The invention relates to electronic control systems of work vehicles. More particularly, it relates to electronically controlled drive systems for skid steer loaders.
Skid steer vehicles such as skid steer loaders are a mainstay of construction work. In their common configuration, they have two or three drive wheels on each side of a chassis that are driven in rotation by one or more hydraulic motors coupled to the wheels on one side and another one or more hydraulic motors coupled to the wheels on the other side.
The wheels on one side of the vehicle can be driven independently of the wheels on the other side of the vehicle, thus permitting the wheels to be rotate in opposite directions on opposing sides of the vehicle, thereby causing the skid steer vehicle to spin in place about a vertical axis that extends upward through the vehicle itself.
The vehicles have an overall size of about 10 by 12 feet, which, when combined with their ability to rotate in place, gives them considerable mobility at a worksite. It is this mobility that makes them a favorite.
Skid steer vehicles commonly have a loader or lift arm that is pivotally coupled to the chassis of the vehicle to raise and lower at the operator""s command. This arm typically has a bucket, blade or other implement attached to the end of the arm that is lifted and lowered thereby. Perhaps most commonly, a bucket is attached, and the skid steer vehicle is used to carry supplies or particulate matter such as gravel, sand, or dirt around the worksite.
One of the disadvantages of traditional skid steer vehicles is their lack of a sprung suspension. The wheels that support the skid steer vehicle chassis are typically fixed with respect to the chassis. They do not move up or down with respect to the chassis, and hence the only shock-absorbing capability they provide is due to the compressions of the wheels. If solid wheels are used, however, they do not even have the compression to absorb impact and cushion travel over irregular terrain.
As a result, skid steer vehicles have been constrained to move at relatively low speeds, seldom above 6 miles per hour, when moving over the irregular terrain of a construction site. Speeds much above this level would permit the vehicle to pitch and roll to a significant degree, which might dump some of the load out of the bucket.
Another reason unsprung skid steer vehicles are limited to low speeds is to give the operator a smoother ride. When skid steer vehicles are operated at speed much over 6 mph, the chassis bounces and rolls so much that the operator experiences a rough and unpleasant ride.
In the last few years, however, manufacturers of skid steer vehicles have begun to add suspensions to their skid steer vehicles. These suspensions permit the skid steer vehicle wheels to move up and down with respect to the chassis. This configuration permits the skid steer vehicles to operate at higher ground speed than the common 6 mph, yet absorbs the ground impacts and terrain irregularities that might otherwise cause significant vehicle bouncing, bucket emptying and operator injury.
Sprung suspensions do have some untoward effects on skid steer vehicle handling under certain operational conditions, however. Skid steer vehicles have a relatively compact wheelbase. They are loaded by filling a bucket and raising the bucket in the air above the operator""s head. The loaded bucket is not disposed at the center of the vehicle, its weight evenly distributed overall four wheels, but is typically cantilevered outward away from the vehicle at the front wheels. In addition to this, a sprung skid steer vehicle can roll and pitch to a much greater degree than an unsprung skid steer vehicle and can also travel at greater speeds over ground, including the irregular terrain of a work site. All of these factors combined could make a sprung skid steer vehicle handle poorly, especially if it carries heavy loads lifted high in the air, and travels at high (+6 mph) speeds over rough terrain,
Other arrangements have been proposed to resist the pitching and rolling of a sprung skid steer vehicle, for example, by restricting the free motion of the vehicle suspension in a variety of ways. While this is beneficial, it does require additional devices that increase the cost and complexity of the vehicle.
What is needed, therefore, is a different system of reducing the pitching and rolling of a skid steer vehicle that limits the vehicle""s turn rate. It is an object of this invention to provide such a system.
In accordance with a first embodiment of the invention, a control system for the drive and steering of a skid steer vehicle having a loader arm capable of carrying a load, the control system is provided, including (i) a means for sensing the amount of load and generating a signal indicative thereof; (ii) a means for sensing the height of the load and generating a signal indicative thereof; (iii) a means for sensing the speed of the vehicle and generating a signal indicative thereof; (iv) a means responsive to operator manipulation for generating an operator vehicle motion command; and (v) an electronic controller coupled to the means of (i), (ii), (iii), and (iv) above, to receive the signals and command therefrom and to generate a drive signal based upon the signals received from the means of paragraphs (i), (ii), (iii), and (iv). The drive signal may control the displacement of at least one positive displacement hydraulic pump. The drive signal may control the displacement of at least two positive displacement pumps. The two positive displacement pumps may include a first positive displacement pump that is fluidly coupled to at least a first hydraulic motor rotationally coupled to and disposed to drive at least one vehicle wheel on the left side of the vehicle and at least a second hydraulic motor rotationally coupled to and disposed to drive at least a second vehicle wheel disposed on the right side of the vehicle. The means for sensing the amount of load may include a pressure sensor capable of measuring the pressure of a tire, the pressure of a loader cylinder, or the pressure of a suspension cylinder. The means for sensing the height of the loader arm may include a loader cylinder position sensor or a loader arm position sensor. The means for sensing the vehicle speed may include a wheel speed sensor, a hydrostatic motor speed sensor, a GPS receiver, a ground sensing laser, or a ground-sensing radar. The means responsive to operator manipulation may include a joystick or a left-hand drive lever and right-hand drive lever. The load sensor may include a sensor disposed to detect the pressure in a loader arm lift cylinder.
In accordance with a second embodiment of the invention, a method of controlling the steering of a skid steer vehicle having a plurality of wheels mounted on the left vehicle side driven by at least a first hydraulic motor and a plurality of wheels on the right vehicle side driven by at least a second hydraulic motor, the vehicle further including at least a first hydraulic pump to drive the at least a first hydraulic motor and at least a second hydraulic pump to drive the at least a second hydraulic motor and an electronic controller coupled to the at least a first and at least a second hydraulic pumps to control their specific displacement is provided, the method including the steps of (i) receiving a signal representative of a vehicle load; (ii) receiving a signal representative of the height of at least a portion of the vehicle load; (iii )receiving a signal representative of the speed of the vehicle; (iv) receiving an operator-generated vehicle motion command; and (v) combining the signals of steps (i), (ii), and (iii), with the command of step (iv) to generate a drive signal. The vehicle further may include at least one loader having a first end and a second end, an implement coupled to the first end and a vehicle chassis coupled to the second end, and further wherein at least a portion of the vehicle load includes a load carried by the implement. The method may include the step of applying the drive signal to a positive displacement hydraulic pump to control the displacement thereof. The step of combining the signals may include the step of derating the vehicle""s response to the operator-generated vehicle motion command. The step of derating the vehicle""s response may include the step of derating the vehicle""s turning rate. The step of derating the vehicle""s response may include the step of derating the vehicle""s rate of acceleration. The step of derating the vehicle""s response may include the step of derating the vehicle""s rate of deceleration.